A mixed penalty-duality formulation of the frictional contact problem, inspired from an augmented Lagrangian approach is proposed. The continuity of the resulting conewise linear operator is used to establish a uniqueness condition on the coefficient of friction. Modified and generalized Newton methods are examined and sufficient conditions for their convergence conjectured. A cylindrical frictional contact problem assesses the stability of the method. Mixed penalty-duality methods are found more accurate and stabler than penalty methods and as economical as them.